The present invention relates generally to a control system for a chiller unit, and more specifically, to a control system for a steam turbine powered chiller unit that can automatically start and stop the steam turbine powered chiller unit.
While most heating, ventilation and air conditioning (HVAC), refrigeration, or chiller systems use electric motors to power the corresponding compressor(s) in the chiller system, some chiller systems can use a steam turbine to power the compressor. Typically, these steam turbine powered chiller systems have required an excessive amount of fieldwork to install and connect the chiller system to the steam turbine system. Some previous steam turbine driven chiller units or systems have involved the packaging of the steam turbine on the chiller unit and resulted in unique installations requiring field routed piping and instrumentation to link the steam turbine system with the chiller unit to complete the installation.
In these previous steam turbine driven chillers systems, many of the controls used with the steam turbine and the chiller unit, e.g., steam turbine governor control, pre-rotation vane control, hot gas control, turbine torque limitation control and surge prevention control, were “stand alone” controls that operated independently of the other controls and did not communicate with the other controls. The use of these separate controls resulted in difficult and complex manual startup and shutdown procedures, as an operator of the steam turbine driven chiller unit had to monitor all of the separate controls and then initiate the appropriate actions on the appropriate controls at the appropriate times to avoid damaging the steam turbine driven chiller unit or having an unnecessary shutdown of the steam turbine driven chiller unit. In addition, the use of these separate controls results in the requirement that the control operations for the steam turbine system be coordinated with the control operations for the chiller unit for a proper startup or shutdown of the steam turbine chiller unit.
An operator of a steam turbine driven chiller system had to perform the following manual operations for starting up or shutting down the steam turbine driven chiller system. During startup, ensure that the turbine casing drain valve is open and then manually open the steam inlet slow roll bypass valve to begin the slow roll warm-up of the turbine. While the turbine is slow rolling, open the gland sealing steam supply valve. After the turbine is warmed up and the vacuum pump started, close the turbine casing drain valve. When the exhaust is evacuated sufficiently for a ramp up to rated speed, open the main steam inlet block valve rapidly enough to ensure that adequate steam is available to increase the speed rapidly through the critical speed band of the turbine to avoid excess vibration. When the chiller is running at rated speed, close the main steam inlet slow roll bypass valve. After any shutdown, close the main steam inlet block valve and the gland sealing steam supply valve and open the turbine casing drain valve.
Therefore, what is needed is a control system for a steam turbine powered chiller unit that can automatically startup and shutdown the steam turbine powered chiller unit.